1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, and more particularly, to trimming of a resistor.
2. Description of the Related Art
In general, laser trimming is performed to adjust the target value of the circuit in analog ICs by matching the resistance value with its intended value.
FIG. 2 is a schematic diagram of a resistor group and fuse elements according to a conventional art.
After two-dimensional patterning of integrated circuits on a semiconductor wafer, electric characteristic of each IC is measured for the whole wafer. From the measured value, a resistance value necessary to output a target value assigned to the circuit is calculated, and trimming cut data is created such that a resistor group 203 in the IC exhibits the necessary resistance value. The resistor group 203 is constructed of resistors 202 which are selectively combined through cutting the fuse elements 201 made from polycrystalline silicon film by laser beam irradiation or the like. The resistors 202 are often made of polycrystalline silicon. Based on the trimming cut data, some of the fuse elements 201 provided in a portion of interconnecting lines are selected to be irradiated with a laser beam and cut off. Laser trimming shown above adjusts the resistance value of the resistor group 203 to a desired value.
Even when laser trimming as the one described above is carried out, however, a problem occurs in which the resistance value of the entire resistor group does not match the calculated resistance value if the relative accuracy differs from one resistor to another. The defect can be a factor for low yield when the IC is actually manufactured. If the cause of the defect is attributed to the polycrystalline silicon resistors formation, the wafer manufacturing process needs to be reviewed. If the cause is attributed to the constituent circuit itself, the circuit needs a modification and a new photomask for producing the IC has to be made. Solving the problem by these methods need some time and money, and are not considered very effective for early resolution for low yield. In addition some increase in cost results in.
An instance of the defect is that the relative accuracy falls in a particular section (region) within a wafer while deviation in relative accuracy occurs always in the same section. FIG. 3 shows an example of a case in which the particular section is a fan-shaped region. Sometimes, a quick action toward the resolution of the defect is required despite difficulties in identifying the cause of the defect only suspected to be in the wafer manufacturing process.